With the advent of the industrial age and the need for inexpensive and readily available fuels, there has been an ever increasing demand upon the oil reservoirs of the world. Such demand has depleted the more easily accessed oil reservoirs and created a need for more cost-effective and efficient methods of recovering well fluids from low production wells.
Accordingly, several potential solutions have been proposed for not only reducing the cost for manufacturing and installing downhole fluid removing equipment, but also for reducing the daily operating cost and maintenance cost of such equipment once installed.
One attempt at improving the cost effectiveness of recovering fluids from low production wells was the utilization of a downhole motor-pump assembly employing a linear motor coupled to a ground surface power source and motor controller by an electrical conduit. While such a solution was satisfactory for some applications, such an arrangement proved to be too expensive in installing and removing such assemblies for repair purposes as the depth of modern wells was extended.
Another attempt at improving cost and efficiency factors in low production wells is disclosed in the above-mentioned patent application Ser. No. 07/462,833, now U.S. Pat. No. 5,049,046. In that patent In that application, there is disclosed, a motor-pump assembly suspended by a cable for coupling power and control signals downhole and for introducing and removing a motor-pump assembly from the well via the production tubing of the well. Such a motor-pump assembly is a highly desirable approach for many low producing wells. While such an assembly and system is desirable it would be highly desirable to have a pump and motor assembly which is easier to transport and to install. In this regard, because of the physical constraints of requiring the motor-pump assembly to be mounted within a production tube having a very small diameter such as approximately two inches, it has proven difficult, if not impossible, to substantially decrease the overall length of such a motor pump assembly while still maintaining its efficiency and thrust or drive producing forces.
For example, while it may be theoretically possible to have a small diameter linear motor that produces a certain drive force, such as a 500 lb. thrust, such a motor would be so long (in excess of 50 feet in length) that it would be unwieldy due to its excessive length. In this regard, such a motor could not be easily and readily transported from a manufacturing site to a well site by conventional and relatively inexpensive transportation. Moreover, because of its unwieldy length the motor-pump assembly would be difficult to mount in the production tube at the well site.
Therefore it would be highly desirable to have a new and improved linear motor which would produce a sufficient amount of thrust to efficiently remove well fluid from a deep well in a cost efficient manner and which could be easily and installed at transported by conventional transportation a well site in a relatively inexpensive manner.